Selenium element and method



:.;:: 5, 1947. A. J. MHLLER. E M.

I SELENIUM ELEMENT AND METHOD Filed Nov. 5,' 1942 nvmvmw mun a. MILLER arm .1. WELLER Patented Aug. 5, 1947 SELENIUM ELEMENT AND METHOD Arthur J. Miller, Newark, and Otto J. Mueller. Rutherford, N.,J., assignors to Federal Telephone & Radio Corporation, Newark, N. 1., a corporation of Delaware Application November 5, 1942, Serial No. 464.6%

This invention relates to selenium elements and particularly to a method of applying .pressure against a selenium coated plate.

The object of the invention is to provide an arrangement whereby a selenium coating can be 3 Claims. (01. 175-386) placed under a pressure without damageto the selenium.

' especially when the pressure is applied for a long time, owing'mainly to the injury done to the selenium by their use. The restriction in the possible number of usable materials is probably due to the fact that a smooth surface must be brought against the selenium and also that whatever substance is used must be non-reactive or non-injurious to the selenium. A good grade of mica sheet has been found satisfactory for the.

purpose, but mica is expensive and not always easily obtainable in a satisfactory form.

In accordance with our present invention, we have discovered that an aluminum sheet can satisfactorily be pressed against the selenium if it is provided'with a hydrated oxide coating of a rather critical quality. By the use of such an oxidized aluminum sheet it is possible to bring the sheet into high pressure contact with the selenium for a considerable period of time, such as a number of hours without injuring the selenium. We have found that if the oxide coating on the aluminum is too thin the selenium is injured or contaminated, apparently by reaction with the surface of the aluminum, and if on the other hand the coating is too thick the selenium tends to adhere to the aluminum more readily than to the base plate with consequent injury to the selenium surface. But by the use of a coating of the proper thickness and qualityit is possible to apply a heavy pressure against the selenium and to heat treat it at the same time fo a considerable time, if desired, and thus improve the characteristics of the selenium.

Our invention will be understood from the following detailed description and the accompanying drawing of which Fig. 1 is a top view of a pressure device for compressing the selenium coated plate; and

the arrangement.

2 In the drawing the disc I is a flat sheet which may be circular, preferably of steel and preferably also nickel coated and roughened in .a wellknown manner to receive a coating of selenium 2. The selenium coating may be applied in any wellknown manner such as by placing selenium powder on the disc and then heating the disc to melt the powder and fuse it to the disc. The disc is shown with a centrally located hole 3 which is customarily used in order to build up a selenium element stack on a mandrel. Plates 4 and 5 represent the pressure plates of a press, the rest of the press mechanism not being illustrated. The plate or disc 6 is the aluminum disc which has on it a coating of hydrated aluminum oxide 1 facing the selenium layer 2. -When the pressure plates 4 and 5 are brought together the hydrated aluminum oxide coating is pressed firmly into contact with the selenium coated disc and a pressure as high as many hundred-pounds per square inch may be applied. At the same time a temperature may be applied if desired as by placing the compressed stack into an oven or if desired by applying a heating element to the heads 4 and 5 of the press. v

We have obtained a suitable aluminum oxide coating by anodizing an aluminum sheet. For the anodizing bath we have found that a sulphuric acid solution with a concentration of' about 10% by weight sulphuric acid is satisfactory, and that the cathode may for example be of-copper, the anode being the aluminum disc or plate which is to be coated with the oxide. We maintain the temperature of the solution preferably at approximately 20 C. We apply a D. C. voltage to the anode and cathode and adjust the flow of current through the solution to be suiiicient to establish an anodizing action. We have found that a current density of about 16.5 amperes per square root of aluminum surface area to be coated is satisfactory, although we have discovered that this can be varied within fairly wide limits, such as from about 4 to 32 amperes per'square foot; and we allow this current to flow for about seventeen minutes at this rate. While the current density to be used is not very critical so long as it is sufficient for the anodizing, the concentration of the solution in combination ,with the time of anodizing is of importance in determining the quality of the coating. If it is not desired to coat the back of the aluminum disc. the coating on the back may be prevented as by covering the back with a material which will not coat, such as styrene. Fig. 2 is a cross-sectional view in elevation of II Although thevalues of the solution concentration and the current flow and time of plating liven in the above 3 method of anodizing the aluminum may vary to some extent, we have found that a serious departure from the directions given abovewilicreatcacoatingoiaiuminum oaide sumciently diiierent from the desired coating to produce trouble when used as a pressure-contact plate over a considerable period of time.

In cases where the pressure is to be applied against the selenium surface for relatively short periods of time, thinner oxide coatingsthan those obtained by the above procedure may be round satisfactory enough. In cases where such thinner coatines may be used the thinner coatings may be obtained by the same anodizing process as described above except that the time of the anodizing in the solution may. be made shorter or the current density may be made less.

What is claimed is: e

i. The method of treating a selenium coated plate which inciudespressing against the top surlace oi theselenium coating a hydrated oxide coated aluminum sheet, the thickness of the oxide coating being in the order 0! that obtained by anodizing the aluminum surface in approximately 10% by weight sulphuric acid solution for about seventeen minutes with a current density between about 4 and 82 amperes per square foot of aluminum. surface to be coated. 4

2. The method of treating a selenium coated late which includes pressing against the top surface or the selenium coating a hydrated oxide coated aluminum sheet, the thickness of the oxide solution for about seventeen minutes with a current density suiilcient tor anodizing. ARTHUR J. MILLER.

O'I'IO J. m.

REFERENCES CITED The following references are oi record in the die ofthispatent:

I UNITED STATES PATENTS Number Name Date 2,203,328 Geisler June 4, 1940 7 2,221,596 Lorenz Nov. 12, 1940 OTHER REFERENCE Anodic Coating of Aluminum, J. n. with. published 1939, Trans Electrochemical Society. vol. 79, pp. 137-144. 

